Place olive oil in Instant Pot and turn to sautée, medium setting. When oil is hot, place bacon in Instant Pot and stir until fried down to desired level of crispiness. Turn Instant Pot off and drain water and fat from bacon and then return bacon to Instant Pot.
Place pasta in Instant Pot, on top of bacon. Add water and place cover on Instant Pot making sure that vent is in "sealing" position. Select manual setting (high) for four minutes. Do a quick release at end of cycle using caution to not get burned from the steam.
Select sauté function (low setting) and use a large wooden spoon and stir in cheese, cream or milk, salt an mustard. The excess liquid will get absorbed by the pasta with a couple of minutes of stirring and a little heat from the sauté feature. If you want to thicken the mac n cheese a bit, sprinkle in a bit of flour to desired consistency.
Serve immediately, or place cover on Instant Pot with vent open and Instant Pot turned to "keep warm" setting. Alternatively, you can place the mac n cheese in an oven safe dish, place it in a warm oven to keep warm or under the oven broiler for a minute or so to brown the top.